The King of Cups represents a just and good man, or a situation involving justice, intelligence, or honor.
Most decks show a mature man, seated on a throne. Sometimes the throne is shown at the shore, or actually floating on water. He may or may not be crowned; most decks show some kind of elaborate headgear with or without a crown. Usually this King is not shown wearing armor; if he is, it’s generally only a token amount, such as just the breastplate. In most decks he is wearing royal robes.
He holds the cup or chalice in his right hand, held by the stem. In some decks he is holding it up as though displaying it to the viewer; in others it is resting on his knee. In many decks, he also holds a scepter in his left hand; whether or not he does, his left arm is resting on the arm of the throne. His attitude is relaxed and casual; he appears at ease with himself. The King’s expression is generally mild; in all respects the aspect of this figure is at the least non-threatening if not actually friendly.
The King of Cups should bring to mind a paternal man, one who is just, and kindly disposed toward the querent. If he is not your father, he does fill the role of a fair and loving father, or has done so in the past. He is someone for whom you feel a genuine affection, and who displays that affection toward you. This is a man who can be trusted absolutely; he favors the querent, and tends to be kind and generous in his relationships in general. Most interpretations also describe the King of Cups as a cultivated and cultured man as well; interested in art and science, and possessing a creative intelligence. If this card does not represent an actual person, then circumstances themselves are highly favorable for whatever endeavor you have in mind.
In the Reading
Upright (or Positive): A just and honest man, who is or has been kindly disposed toward the querent. Responsible and mature, he displays paternal feelings toward the querent. He is intelligent and probably cultured and well-educated as well; and as a result has skills and connections that you need at this time. His appearance in the reading indicates that he is willing to help you in some way; or will be willing if asked for help. If the card does not represent a person, then the situation involves justice, honor, learning and understanding, intelligence and intelligent action; in short, authority fairly used.
Reversed (or Negative): A deceitful man; one who cannot be trusted. A dishonest, double-dealing man who will trick you, or cause losses in personal relationships or career. Injustice, vice, scandal in the offing.
Note that negative readings on the court cards are still positive in their own way. They indicate that this is someone that you do or will love or trust, but you are being warned not to, for your own good.
From Tarot for Beginners, by P. Scott Hollander